Increasing efforts to manage gas emissions from animal feeding operations is expected to lead to a demand for an economical and effective method for assessing mitigation practices. The purpose of this project was to compare gas concentrations measured using semi-continuous gas sampling with dedicated gas analyzers versus those obtained using a sampling system that filled 50 L bags over 24-hour periods. Sampling was done on two biofilters treating air from a swine nursery at the West Central Research and Outreach Center at Morris, MN. Percent reductions calculated using inlet and outlet concentrations determined using both methods were compared too. Results indicate that the 24-h bag sampling method concentrations and percent reductions tracked the semi-continuous sampling method concentrations and percent reductions well. Ratio means for NH3, CO2, CH4 and N 2O were close to one indicating similar concentrations using the two methods. The H2S ratio mean was near 0.71 which indicated that 24-h bag concentrations were typically 29% less than the corresponding concentration measured using semi-continuous sampling. Mean percent removal differences for all five gases were within ±0.05 of zero which indicated good agreement between the two methods. Additional evaluation of the 24-h bag sampling method is ongoing.